1. Field of the Invention
The invention relates generally to a current-perpendicular-to-the-plane (CPP) tunneling magnetoresistive (MR) sensor, and more particularly to a CPP-TMR sensor with s pinned layer that extends beyond the stripe height (SH) and optionally the trackwidth (TW) of the free layer, and to a method for making the sensor.
2. Background of the Invention
One type of conventional current-perpendicular-to-the-plane (CPP) magnetoresistive sensor used as the read head in magnetic recording disk drives is a magnetic tunnel junction sensor, also called a tunneling MR or TMR sensor. A TMR sensor has a stack of layers that includes two ferromagnetic layers separated by a tunneling barrier layer, i.e., a nonmagnetic electrically insulating spacer layer, which is typically MgO. One ferromagnetic layer adjacent the spacer layer has its magnetization direction fixed, such as by being pinned by exchange coupling with an adjacent antiferromagnetic layer, and is referred to as the reference layer. The other ferromagnetic layer adjacent the spacer layer has its magnetization direction free to rotate in the presence of external magnetic fields from recorded data on the disk and is referred to as the free layer. With a sense current applied perpendicularly through the sensor layers, the rotation of the free-layer magnetization relative to the reference-layer magnetization due to the presence of external magnetic fields is detectable as a change in electrical resistance.
In a CPP-TMR read head, the magnetization of the reference layer is generally orthogonal to the disk-facing surface and the magnetization of the free layer, in the absence of external magnetic fields, is parallel to the disk-facing surface. A CPP-TMR read head may have an extended pinned layer, meaning that the reference layer extends beyond the free layer back edge, i.e., the edge recessed from the disk-facing surface. The reference layer may also extend beyond the free layer side edges in the trackwidth direction, i.e., the direction parallel to the disk-facing surface. However, the conventional method for making a CPP-TMR read head with an extended pinned layer often results in a back edge having an undesirable profile and with removal of a portion of the reference layer. Variations in the profile of the back edge can result in an inaccurate stripe height, i.e. the free layer dimension between the disk-facing surface and the back edge, and removal of a portion of the reference layer can adversely affect the pinning of the reference layer.
What is needed is a CPP-TMR sensor that has a free layer with a precise back edge and an extended reference layer with no material removal, and to a method for making the sensor.